1. Problems
Instruments are often used to measure air and water parameters such as temperature, humidity, pressure, air velocity, airflow, and many other environmental parameters. These measurements take place in buildings, factories, outdoor weather stations, and other locations. Instruments may be rack-mount, desk mount, mobile/handheld, or other.
A typical instrument consists of a plastic case enclosing a printed circuit board with microprocessor-controlled electronics, memory, one or more sensors, and a display. The sensors are often in a wand-shaped probe. Various probes, large and small, are designed to collect environmental samples for sensing, measurement, display, and storage. When using this type of instrument, a user has both of his hands occupied, one to hold the meter, and one to hold the probe and extend it to the location of interest, such that a user's hands are not available for other tasks. Cables, wires, and/or tubes typically dangle between the probe and the meter.
For Heating, Ventilation, Air Conditioning, and Refrigeration (HVAC) applications, engineers and technicians who work in buildings deal with many different types of instruments. There are building automation systems (BAS), fire safety systems, occupancy detection and security, permanently installed instruments such as pressure, temperature, humidity, and airflow, with some nearby and some remote sensors, and portable instruments for such parameters as temperature, pressure, humidity, sound/noise, light intensity, carbon dioxide, velocity, flow, and others. As engineers and technicians move throughout the structure to solve problems, they often lack access to required information, and must either move to a central location for access to data, or must carry a variety of instruments with them. Lacking is an overall system for quick access to desired information.
Engineers and technicians commonly require two types of measurements. One is immediate feedback when finding and/or solving a problem, as when measuring the temperature of air being supplied at a diffuser. The second is a series of measurements at regular intervals from one or many locations, for comparison and contrast of parameters that may indicate problems that occur over time.
Measurement problems are important to the HVAC industry. Measurement disputes are often at the heart of conflicts over HVAC performance issues such as uncomfortable buildings, inefficient energy performance, and inability to maintain specified parameters such as adequate positive pressure in hospital operating rooms. These conflicts frequently result in anger, confusion, disputes, cancelled contracts, lawsuits, mediation, and unhappy building owners, tenants, and workers. Contributing to these conflicts is that measurements of HVAC-related building parameters such as air and water temperature, humidity, pressure, velocity, and flow are perceived to be inaccurate and unreliable, so dissatisfied parties often challenge their validity. Accordingly, an improved system and method that improves the accuracy and speed of measuring building parameters and the safety with which they are measured by technicians are desired.
Flow, airflow, and water flow are industry terms that relate to the volumetric rate of fluid flow expressed in units such as cubic feet per minute (CFM) or gallons per minute. Airflow is usually not measured directly. It is usually calculated by measuring the velocity of air at multiple points in a cross-sectional plane, calculating an average velocity at the plane, and then multiplying by the known area of the cross-section. The plane where measurement takes place might be across an air duct, in a duct-shaped probe like a capture hood, or at the opening of a fume hood, door, or window.
These are long standing problems in several different measurement applications related to HVAC.
Exemplary Problem 1. Wasteful Back and Forth Travel.
Technicians are concerned with the occupied spaces and the system controls that are spread all over the building, from the facilities space with the fan, coils, pumps, pipe, compressor, and/or evaporation tower, through the duct system to the occupied spaces. In many cases the point of interest to an operator or technician is some distance removed from the forces or controls that cause the conditions at the point of interest. To adjust the controls for improved operation requires a lot of back and forth movement during a repetitious cycle of measurements and adjustments. They must measure at one location, then move to another location to effect a repair or adjustment. Then they must return to the original location to measure the impact of the change. This wastes time and leads to approximations. What is needed is real-time data at the point of control, so changes can be readily evaluated and adjustments made precisely as specified.
Exemplary Problem 2. Poor Communication within Teams.
A second problem of conventional practice in HVAC measurements relates to technicians who work in teams of two or more. Measurements are usually taken by one person. Team members who need the information must receive it from the one who took the reading, usually by speaking, shouting, or walking to a conference, or sometimes via walkie-talkie or cell phone.
Exemplary Problem 3. Instrument Limitations.
A third problem with existing instruments is that they provide limited information with each measurement. For instance, during a velocity traverse of an HVAC duct, the technician may need to record a series of air velocity measurements, plus the air temperature, air humidity, barometric pressure, and the duct static pressure. The meter he uses may display only one of these parameters at a time. Further, he may have to change the setup of the meter between measurements to acquire all of the necessary information. Accordingly, an improved system and method to provide technicians with more of the information relating to a particular application are desirable.
One reason for this problem is that general-purpose instruments are being used for applications that are specific to operations such as air balancing. For instance, a differential pressure meter is attached via rubber tubes to a Pitot tube, and the combination used to determine the air velocity in the duct. It is desirable to have a tool designed specifically for HVAC applications such as duct velocity traverse.
Engineers and technicians do not have one system of convenient access to required information. Instead, they often use a wide variety of instruments, including BAS, temperature meters, humidity meters, air pressure meters, water pressure meters, air flow meters, water flow meters, etc. It is desirable to have the capability to quickly access any required measurement as they move throughout a building to find and fix problems. It is desirable to have a system and method that allow engineers and technicians to measure immediately and interactively, while also providing means to datalog the same measurement types at the same locations at regular intervals over a period of time.
Exemplary Problem 4. Instrument Style.
A fourth problem in conventional practice has to do with the size and shape of instruments and the intended method for taking measurements. Many instruments are designed in the form of a hand-held probe attached with a coiled cord to a handheld meter. Taking a measurement occupies a technician such that he cannot do anything else with his hands at the same time. In connection with the measurements taken, it is often necessary for a technician to use his hands to climb a ladder, drill holes, screw or unscrew, or move a lever. A technician may have to set down an instrument in order to effect a repair or make an adjustment, and in so doing will lose sight of the meter readings. The existing type of instrument is clearly cumbersome in this context. It is desirable to have instruments that are relatively small, relatively light in weight, and easy to manipulate in the environment of interest. I
Exemplary Problem 5. Instrument Size and Weight.
Airflow capture hoods are used to collect the air being supplied by diffusers. One popular capture hood weighs 10 pounds and must often be held tightly against a ceiling diffuser. If the ceiling is high, the technician must employ a ladder. This type of procedure is difficult for most people to perform properly hour after hour, day after day. Fatigue, strain, and injuries are common. It is therefore desirable to have instruments that are relatively small, relatively light in weight, and easy to manipulate in the environment of interest.
Exemplary Problem 6. Accuracy and Reliability
As a result of Problems 1 through 5, measurements are often performed too quickly, improperly, inaccurately, or not at all, due to short cuts taken by technicians under stress. For instance, a technician who realizes that a measurement is likely because of circumstances to be inaccurate or unrepresentative is more likely to compromise, estimate, or skip the measurement. It is desirable to have instruments that are quick and easy to use and that can be trusted to achieve an accurate result.
Exemplary Problem 7. Manpower.
Current practice is to use two-man teams, for some of the reasons listed above: safety; heavy, cumbersome instruments; working above the ground on ladders or scaffold; needing to be in two places for measurements and control adjustments. Accordingly, systems and methods that require less manpower are desired.
Industry Applications
The following use cases are some industry procedures that illustrate the long standing problems mentioned above.
Set Point of Duct Static Pressure
In HVAC duct systems it is important to maintain duct static pressure setpoints at various locations in a duct system in order to maintain airflow through the duct and diffusers. For instance, a building engineer might specify that the fan generate a duct pressure that is 3 inches of water column above the ambient pressure in the building (static pressure), that the secondary supply air ducts that feed each floor be maintained at 2.5 inches of water column, and that the system of valves and dampers be adjusted such that the most remote air diffuser will be supplied air at a pressure of at least 0.5 inches of water column. If pressure is too low, the diffusers will not distribute conditioned air as designed and building comfort will suffer. If pressure is too high, energy is wasted by running the fan too fast. The electric power used increases at the cube of the duct pressure increase. For instance, if the fan speed is increased to raise the remote duct pressure to 0.55 inches, only 10% higher than required, the fan will use 30% more electric power than required. (The calculation has the form of 1.1×1.1×1.1==1.3.)
Current procedure requires a technician to measure the pressure, then move through the building to adjust the fan and the dampers. He then returns to measure pressure again. This cycle of measurement and adjustment will be repeated until the specified result is achieved. Sometimes the fan is a long distance from the point being measured, and on a different floor. This repetitive procedure requires a lot of time and effort, and leads to the technician settling for some safe guard-banded pressure instead of achieving the precise result desired. This is one of the main sources of wasted energy in buildings. It is desirable for applications like this to provide a technician with a an improved system and method for making measurements at the point of interest, and delivering results continuously to him where and when he is making the adjustment at the point of control.
Setting Outside Air Ventilation Controls
One of the most important functions in HVAC is to provide adequate ventilation, which is done by bringing in fresh air to replace used air that is infused with odors, body moisture, carbon dioxide, and other products of the indoor environment. This is a health issue, not just a comfort issue, and is strictly regulated. The volume of outside air needed is calculated according to industry formulas. Then the outside air dampers and control fans are adjusted by a degree estimated to achieve the correct volume.
This procedure often involves the measurement of several temperatures: outside air, indoor supply air, indoor return air, and the air inside the mixing chamber. The temperature in the mixing chamber is related to the temperature of return air and outside air, and the volumes of each. Adequate ventilation can be determined by measuring and comparing the different temperatures. Adjustments are made, and then the four temperatures are measured again. This is repeated until the mixed air temperature reaches a specific function of outside air and return air temperatures. Needed is a way to measure all four of these temperatures concurrently, and provide them in real time to the technician at the point of control, so he can quickly see the result of his adjustment.
Damper Setting and Proportional Balancing Method
Two technicians generally work together to adjust dampers to set airflow through supply diffusers to match specifications. One tech lifts up and holds a capture hood airflow probe against the diffuser, which is usually on the ceiling. He reads a meter attached to the capture hood. He calls out the reading. The second technician climbs a ladder and locates the damper adjustment above the ceiling tiles. He adjusts the damper until the measurement called out meets the specification. Needed is a way for the person doing the adjusting to be able to see the results of the adjustment in real time.
The meter must measure the temperature of the supply air in order to make an accurate reading. However, it takes a long time for temperature probes to properly register the actual temperature of air coming out of the duct, so technicians often ignore this requirement. Needed are means for quickly measuring the actual air temperature and using it to improve the accuracy of the measured airflow.
Also needed is a way for one person instead of two to perform this task. A stand or jack can be employed to hold the capture hood against a ceiling diffuser. This helps prevent the heavy and bulky hood from losing a seal, and it prevents weariness and injury to the operator. However, it is still necessary for the adjustor to have the measurement shouted over to him, or, if working alone, for him to leave the damper, climb down from the damper, walk to the capture hood, see the result on the meter, and return to the damper to make another adjustment.
A related industry method is the Proportional Balancing Method. Specifications often require that supply air diffusers be adjusted so that their airflows are all the same percentage of the specified airflow. For instance, if there are three diffusers, and the air available is 10% less than specified, then each air diffuser should be set to 90% of the specified flow. If the specified flows were 300, 200, and 100 cubic feet per minute (DFM), then the post-adjustment measurements should be 270, 180, and 90 CFM. However, duct systems with dampers and supply diffusers and return grills have paths to resistance of airflow that are interrelated. That is, if one path is made more resistant to airflow by adjustment of a damper, the air adjusts and goes somewhere else. This makes it difficult to set dampers the way they should be set. Usually the diffuser furthest from the fan is set by adjusting its damper. Then a second damper is adjusted. Then, the first diffuser must be measured again to determine if the second adjustment caused such a change in duct airflow distribution that the first diffuser airflow became out of range. The two dampers are adjusted again until they are both in spec. Then a third damper is adjusted. This continues until all diffusers on the same branch of the duct system are within the specified range. This takes a long time, with many repeated measurements. Each diffuser must be measured independently, one at a time, despite the fact that they are part of a connected and interdependent system. This method is repetitious and wastes time. It leads to compromise and non-ideal outcomes. What is needed is to see the effect of changes in real time.
Evaluation of Thermal Transfer Coil Efficiency
It is often important to measure the moisture content of air in ducts. A critical HVAC function is thermal energy transfer via coils. For instance, energy is used to remove moisture and cool air from outside that enters hot and humid. HVAC technicians must measure the temperature and moisture content of air before and after it is exposed to the bank of coils in order to determine whether the system is performing properly. Then the system is exercised to vary the load on the coils while measurements are taken. Needed for this application are means of concurrently viewing the incoming air temperature and humidity as well as the outgoing air temperature and humidity.
Water-Side Balancing
In HVAC machine rooms there are pipes running to and from the chillers, evaporators, pumps, and valves. It is necessary to measure water temperature and pressure in various places. These measurements are related to each other. At present is it time consuming to make iterative measurements between many adjustments to pump speeds and valve setting. Needed are means to see a variety of water pressures, temperatures, and water flows concurrently.
Velocity Traverse of Air Duct
The volume of air moving through a system of ducts is a frequently required figure in HVAC. System designers specify the air characteristics at specific locations throughout the duct system: leaving the fan, passing through filters and coils, delivered to the main duct on each floor, branch ducts, and finally supply air diffusers. The same is true for the return path to the fan intake, which begins at return air grilles in the occupied spaces, then past return air fans and dampers, mixing chambers where outside air enters, and into the main air handler intake. At each of these key points in the system, air balancers measure airflow volume, temperature, humidity, and duct static pressure.
Airflow volume is not measured directly in a duct. Instead, the average velocity of the air is determined and multiplied by the cross-sectional area of a plane across the duct. Since the velocity of air varies significantly over such a cross-sectional plane, an average velocity must be determined by measuring many different locations in the cross-sectional plane, and then averaging those values. The industry has derived standards for the locations to be measured, that are specified in terms of the distance from the duct walls.
A technician first measures the length and width of a rectangular duct, or the diameter of a round duct, and calculates the cross-sectional area, adjusting for the thickness of the duct walls and any insulation or other internal obstructions. Then he consults a table provided by an engineering society such as ASHRAE for the locations of the points in a matrix on the duct cross-sectional plane. The technician drills holes in the duct to allow the Pitot tube to be positioned at the each point in the matrix. It is convenient to think about horizontal and vertical planes across the duct. The technician marks his probe with tape so he can see how far into the duct to insert it to reach each traverse point. Then he makes a velocity measurement at each traverse point, one after the other, recording or storing each reading as he goes. In most cases it is necessary to measure between 16 and 150 different traverse points. This is a laborious and error-prone operation.
During a duct velocity traverse, a technician stands high on a ladder with his head in the dark space above the ceiling tiles. With traditional equipment, he holds a meter in one hand and a velocity probe such as a Pitot tube in the other hand. Between the meter and the Pitot tube are rubber hoses that dangle down and are prone to getting caught on projections. The hoses are also prone to swinging during measurement, which can affect the accuracy of the measurement.
A proper velocity measurement also requires determining the air density. Density in turn requires barometric air pressure, temperature, and if possible, humidity. Barometric pressure is easily measured inside the meter and is not a problem. Temperature and humidity present another problem for a technician. Already burdened by meter, probe, and dangling tubes, he must manipulate a temperature probe from the meter into the duct and keep it lodged there while performing the 16 to 150 separate velocity measurements mentioned above.
Once the velocity traverse has been completed and the Pitot tube withdrawn from the duct, a technician performs a separate setup to prepare to measure duct static pressure. A traditional meter must be removed from a Pitot velocity mode and placed into a differential pressure measurement mode. Then the user changes the hose connections between the Pitot tube and the meter. Finally, the user reinserts the Pitot tube into the duct and performs the static pressure measurement.
In summary, the airflow, velocity, temperature, and pressure measurements required are difficult and time consuming to obtain using traditional instruments and methods. Such a measurement process may require three different duct insertions, three different measurement modes on the meter, and two different hose configurations. The bulky meter may weigh a few pounds, and the user may have difficulty manipulating it with one hand to press the control keys while manipulating the Pitot tube with the other hand and keeping the tubes and temperature probe from swinging and getting tangled.
2. Description Of Related Art Existing Products and Technologies
Recently some wireless meters have appeared (e.g., Testo) eliminating the conventional coiled cable between the probe and the main body of the meter. However, one hand is still necessary to hold the meter, and another is required to hold the sensing probe. The sensing probes are still as large and ungainly as conventional instruments. They can be placed and left on a desk or file cabinet or floor, but are difficult to place at the point of interest for HVAC technicians, such as slotted air diffusers or water pipes.
Another type of wireless device has been used in HVAC applications. This is a wireless sensor network for datalogging, collecting environmental data at regular intervals. For example, at intervals of 10 seconds or one minute, a sensor makes a measurement and transmits it wirelessly to a stationary data collection and storage point. Once in a while the collected and stored data can be loaded onto a computer for analysis. The network data collector's memory is erased and a new set of data collection begins. This type of system is used to monitor buildings and factories. An example of this type of instrument is Wizard from Dickson. While useful for some tasks, the system has drawbacks. It requires a personal computer to display the results, so it is cumbersome to move around a building. The sensor modules are shaped for mounting on a desk or file cabinet or other flat place, but are not convenient for air diffusers and pipes.
In a quite different industry, medical monitoring of vital signs, wearable wireless instruments have appeared. These collect measurements such as blood pressure or pulse rate and wirelessly transmit the results to a nearby data collector or to the wrist of the user. From there results can be viewed or sent to a monitoring system for review or alarm. A related module might sound an alarm to the person wearing the sensors to alert them to excessively high blood pressure or similar problem. However, this type of instrument is not useful for finding and fixing HVAC problems, because it does not provide for remote sensors measuring environmental conditions.
Another interesting wireless application is wrist-mounted displays for runners and other athletes that show data from sensors mounted in their shoes or on their bodies to provide a measure of their performance. These systems lack remote sensors that measure environmental parameters, as well as other features that are applicable to HVAC and other industrial applications.
Problem Summary
To summarize the general problems with traditional instruments and methods, they limit the productivity of technicians by being heavy, cumbersome, by not measuring all of the required parameters simultaneously, by restricting the availability of measurement data among team members, and by forcing repeated movement between the points of cause and effect. Measurement procedures take much longer than desirable. Time is wasted. These problems lead to short cuts by technicians, which in turn product inaccurate or misleading measurements that have little credibility among industry peers.
Accordingly, improved apparatus, methods, and systems for measurement of environmental parameters are desired.